Cardiovascular diseases are responsible for a large amount of deaths around the world and are a major burden on the health care system. Cardiac transplantation is still the best treatment available for end-stage heart disease. However, besides the high costs for this intervention, restrictions of the procedure relate to the sides effects derived from the use of immunosuppressants and the limited availability of organ donors. Among other possibilities, cell transplantation has emerged as a novel tentative option to stimulate myocardial regeneration. By reducing the need for organs, cell-based treatments will be of great importance to both society and to the individuals suffering from severe degenerative diseases such as cardiac infarction.
The traditional view of the heart as a post-mitotic organ has been challenged during the past few years and myocytes turnover as well as the presence of stem/progenitor cells residing in the adult mammalian heart has been described (Urbanek et al PNAS 2003, 100 (18), 10440-45, Laugwitz et al Nature, 2005, 433, 647-653, Messina et al Circ Res 2004, 95, 911-921, Beltrami et al Cell, 2003, 114, 763-776, Cai et al Dev Cell 2003, 5, 877-889). A number of different tissues have been proposed as the source of stem cells able to generate new cardiomyocytes (e.g. fetal cardiomyocytes, skeletal myoblasts, bone-marrow derived stem cells, stem cells isolated from umbilical cord blood, adipose tissue derived stem cells, and embryonic stem cells). So far only embryonic stem cells have been shown in vitro to efficiently differentiate into spontaneously contracting cardiomyocyte-like cells (Kehat et al J Clin Invest, 108: 407-414, 2001, Xu et al Circ Res, 91: 501-508, 2002, He et al Circ Res, 93: 32-39, 2003, Mummery et al Circulation, 107: 2733-2740, 2003). However, derivation and isolation of cardiac stem cells or MCP cells from human blastocyst stem cells have not been previously described. Notably, MCP cells are immature cells that not yet have acquired the functional features of cardiomyocyte-like cells.
On the other hand, cardiac stem cells were reportedly isolated from human post-natal heart biopsies and propagated in tissue culture (Messina et al Circ Res 2004, WO2005/012510 A1, WO2006/052925 A2). These cells were clonogenic, expressed stem and endothelial cell markers (e.g. c-kit, CD-34, Sca-1), and were able to differentiate into myocytes, endothelial and smooth muscle cells in vivo. These isolations however are depending on the accessibility to human biopsies and surgical techniques for their retrieval.
A number of reports have demonstrated the capacity of human embryonic stem cells to differentiate into contracting myocytes but no report has so far identified and isolated a discrete intermediate cardiac progenitor cell population from human embryonic stem cells.
There is a great need for a simple non-surgical method for derivation, isolation, and expansion of cardiac progenitor cells for subsequent use in pharmaceutical drug development, toxicity testing, and cellular therapy.